Salmonellosis is one of the most common and wide spread food diseases caused by bacteria of the Salmonella spp. genus. It has been estimated that Salmonella spp. is responsible for more than 1.4 million cases of enterocolitis and more than 500 deaths per year in the United States.
The current taxonomic system of Salmonella spp. has regrouped all the strains of Salmonella spp. (pathogenic or not) into two single species: S. enterica and S. bongori. The latter (previously subspecies V) does not seem to be pathogenic for human beings.
S. enterica species has six subspecies (sometimes as subgroups under Roman numerals): enterica (I); salamae (II); arizonae (IIIa); diarizonae (IIIb); houtenae (IV); S. bongori (V), already included in a different species; and indica (VI).
Each subspecies is in turn formed by different serotypes, up until now more than 2,500 being identified. One of them is S. enterica subsp. enterica (or subgroup I) which is divided into five serogroups: A, B, C, D and E. Each serogroup in turn comprises multiple components, giving rise to serovars (serotypes).
With clinical epidemiological importance, the more than 2500 serovars of Salmonella spp. can be grouped into three ecological divisions (spp. are subspecies):                1. Salmonella spp. adapted to live in human beings, among them, S. Typhi, S. Paratyphi A, B and C;        2. Salmonella spp. adapted to non-human hosts, which circumstantially can cause infections in humans, among them, S. Dublin and S. Choleraesuis;         3. Salmonella spp. without specific host adaptation, which includes 1,800 serovars widely distributed in nature, which cause most cases of salmonellosis worldwide.        
The typical detection of this pathogen includes procedures based on the culture and biochemical identification of colonies. The standard operating procedure based on the culture requires seven days to confirm the presence of this pathogen in the sample analyzed. Although these procedures are efficient, they are too slow to be used systematically in a large number of samples.
As an alternative to the procedures based on the culture and biochemical identification of the colonies of Salmonella spp., there are a number of techniques for the detection of said pathogen based on PCR (polymerase chain reaction) technology. Furthermore, by means of said technology it is also possible to detect live cells if starting from RNA to perform PCR or live and dead cells if starting from genomic DNA.
U.S. Pat. No. 6,893,847 describes oligonucleotides especially designed for detecting mRNA of the Salmonella spp. invA gene.
Fey et al. (Applied and Environmental Microbiology, 2004 vol. 70(6): 3618-3623) have developed a method for the detection of bacterial RNA in water sample based on the use of real time PCR. To test the developed method, invA gene and 16S rRNA of Salmonella enterica serovar Typhimurium are used.
Fukushima, H. et al. (Journal of Clinical Microbiology, 2003, vol. 41(11): 5134-5146) describe a Duplex Real Time PCR assay using SYBR Green for the detection of 17 species of pathogens present in water and food starting from genomic DNA. Salmonella spp. is among the pathogenic species detected. Primers targeted at amplifying the Samonella spp. invA gene are used for its detection.
Furthermore, methods allowing the detection of multiple Salmonella spp. species and serovars have also been developed in the state of the art by means of a single PCR reaction:
Nam, H. et al. (International Journal of Food Microbiology, 2005, vol. 102: 161-171) describe a Real Time PCR assay using SYBR Green for the detection of different Salmonella spp. species (see Table 1 of said publication) starting from DNA. To that end they have designed a pair of primers which specifically amplifies a 119 by fragment of the Salmonella invA gene.
Patent application EP0739987 describes a method for the detection of different Salmonella spp. species from DNA by means of a PCR comprising the use of oligonucleotides specifically targeted at the Salmonella spp. invA gene.
Rahn et al. (Molecular and Cellular probes, 1992 vol. 6: 271-279) describe a method for the detection of multiple Salmonella spp. species from DNA comprising the amplification of the sequence of the Salmonella spp. invA gene by means of a polymerase chain reaction.
Therefore, there is in the state of the art a need to develop a method for the detection of Salmonella spp. which allows detecting a large number of serovars of said pathogen and which is in turn efficient, fast and cost-effective.